In an electro-optical thermal viewing and targeting system there are typically provided a radiation sensing device, such as a FLIR (Forward Looking InfraRed sensor), typically being sensitive to radiation in the infrared and a laser designator, emitting radiation in the near or medium infrared range at a wavelength different from that of the FLIR. In order to ensure that the image on the radiation sensing device reflects the position of the laser, it is necessary to ensure that the lines of sight of the laser and the FLIR are parallel. This is known as boresighting.
A conventional laser boresighting system focuses a portion of the laser energy onto a heat conductive element, such as ceramic, so as to cause it to become heated and thus emit thermal energy in the range of sensitivity of the FLIR. The thermal energy is focused onto the FLIR along an axis having a predetermined orientation relative to the line of sight of the laser. The thermal image thus produced on the FLIR provides an indication of the correlation of the respective lines of sight of the FLIR and the laser.
The system described requires that there be an optical path between the laser and the FLIR. Furthermore these systems suffer from a problem of synchronization between the laser and the FLIR since the pulse length of the laser is much shorter than the scan time of the FLIR.